1. Field of the Invention
The invention relates to a catheter. The invention relates in particular to a catheter for ablation in body cavities such as blood vessels or organs such as a heart.
2. Background Art
It is known to perform treatments in a human or animal body with the aid of catheters having an electrically conductive first end. This ablation electrode is typically present on the end of the catheter. There are also embodiments with several ablation electrodes one behind the other on the catheter which is inserted into said cavity. The patient is then laid on a conductive plate, for instance a grounding plate. Then, an electric current is passed through the catheter, which current flows through the body. If the first end is held against or at a very short distance from a wall of the body cavity, said wall will be heated locally over a relatively small area as a result of the electrical resistance of the wall. Consequently, ablation occurs in said area. As a result thereof, part of the tissue of said wall dies. With this treatment, for instance cardiac arrhythmias can be treated and prevented in the future.
During this known treatment, it is of importance that the temperature of, in particular, said first end of the catheter can be controlled in order to evaluate the amount of warming of the target area; hence, based on inter alia this temperature, the power which is to be supplied to this first end can be controlled. Moreover, prior to the actual treatment, with the aid of a relatively small amount of power, the abutment of said first end against the wall can be assessed based on the temperature increase which is measured in said first end. In fact, a poorer abutment will lead to a smaller temperature increase when the power supplied remains the same. Moreover, the temperature in the fluid, in particular blood, is to be prevented from rising too much around said first end because clogging can occur as a result thereof, which clogging can lead to dangerous situations in the body. Moreover, too strong a heating of the first end of the catheter can lead to blistering, explosions due to boiling of entrapped liquid in the wall of the respective cavity such as the heart, which is dangerous to the health and, in extreme cases, can lead to openings in the heart wall. Furthermore, the danger exists that undesirably large areas are affected, as a result of which damage to, for instance, an AV- node can occur. In order to be able to measure this temperature, it is known to include a temperature sensor such as a thermocouple in said first end.
In order to prevent said first end of the catheter from being heated too strongly, it has been proposed to cool this first end. To that end, Wittkampf (Journal of the American College of Cardiology 1988, 11, p.17A) has described a catheter wherein a fluid channel is provided in the catheter, which channel terminates in outlet openings in said first end. A cooling medium such as physiological saline solution can be forced through said channel and provides continuous cooling of said first end during use. Thus, the temperature thereof can be kept low. However, a disadvantage of this known catheter is that the actual temperature of said first end cannot be accurately measured.
In order to solve this disadvantage, it has already been proposed to also include a thermocouple in said first end in such a catheter. However, as a result of said cooling, this temperature reading is inaccurate. Consequently, the temperature change of said end and, hence, of for instance the fluid, in particular the blood around said first end or the temperature of the wall, cannot be verified sufficiently accurately, so that clots can still occur. Moreover, the extent of the temperature increase of the wall cannot be sufficiently controlled and verified. Because the first end of this catheter remains relatively cool, no deposits of such clots will be detected on said exterior, which entails the risk that it can be wrongfully assumed that no clots have formed during the treatment. In fact, the fluid, in particular the blood around said first end and/or the wall, may very well have been heated such that coagulation has occurred, resulting in clots.
In an alternative known embodiment, a catheter is provided with a closed channel extending through said first end, with which the first end is cooled from the inside. Here, the same dangers arise as with the above-described catheter. Moreover, the great drawback is that the blood is not cooled at all.